Motor control units for use in drive systems for motor vehicles usually have functions which may be used to detect incorrect calculations of internal variables and control variables. Multilevel concepts are usually provided, system states being ascertained in a first level, the control level, and a default variable being evaluated, for example a driver-requested torque as an indication of a position of an accelerator pedal, and a setpoint torque being ascertained therefrom. The setpoint torque is converted into one or multiple corresponding control variable(s), depending on the type of drive motor. In the case of internal combustion engines, these control variables may include the fuel quantity to be injected, the point in time of injection, the air supply and the like. In electromotive drive systems, the control variable may correspond to, for example, a motor current.
In a second level, referred to as the monitoring level, the setpoint torque is redundantly ascertained according to the functions of the first level. However, instead of calculating the control variable from the setpoint torque, the control variable is read back from an output stage with the aid of a corresponding function in the monitoring level, and an actual torque provided by the drive motor is ascertained therefrom with the aid of a calculation inverse to the control level. The monitoring level then ensures, on the one hand, that the setpoint torque ascertained in the control level is limited by a monitoring torque ascertained in the monitoring level and, on the other hand, that the conversion of the setpoint torque ascertained on the control level into the corresponding control variable is checked by calculating an actual torque, which corresponds to the driving torque actually provided, from the control variable read back from the output stage. By comparing the back-calculated actual torque with the setpoint torque ascertained in the first level, it is possible to identify an error during conversion of the setpoint torque predefined on the control level into the control variable.